1. Field of the Invention
The invention relates to a process for removing impurities from granulated material such as abrasives for cleaning workpieces or powdered welding flux for welding machines, and to a device for applying this process.
2. Description of the Prior Art
In processes carried out by using granular working substances, that is, granulated materials or mixtures thereof, it is customary to circulate these materials, remove incidental impurities from them during circulation, and replace the consumed granulated materials with fresh ones.
The operation of generally known centrifugal wheel cleaning machines in which customary granulated material reprocessing plants have been employed may serve as an example. The granular cleaning agent emerges from an intermediate hopper after a hinged door has opened, falls under gravity to the centrifugal wheel and after this operation has been completed is lifted together with the impurities formed from a receiving hopper below to a granulated material cleaner, as for example by means of a bucket elevator, and is there cleaned. Of the two suction fans customarily present, one, usually mounted on the granulated material cleaner, is used to remove dust from the granulated material and the other, usually mounted on the remove dust filler, is used to remove dust from the cleaning chamber. With centrifugal wheel cleaning machines such as this, which must be shut off and opened each time a workpiece or charge is changed, fresh granulated material is introduced into the cleaning chamber manually as required to replace the granulated material consumed, while the machine is shut down.
UP welding machines are another type of generally known mechanism with circulating granular working substances. Simpler versions are usually equipped only with a granulated material or powder bin and an exhaust system. When a charge of granulated material has been introduced, operation continues for a certain amount of time, after which the welding process is interrupted and a charge of fresh granulated material is introduced manually. Such machines are unable to meet the operating requirements of modern welding systems; in addition, they produce widely varying welding flux compositions.
More complex welding systems with a fresh granulated material or fresh welding flux supply feature have thus far generally been designed as follows: the circulating welding flux is drawn upward by means of a suction fan from the welding head to a centrifugal separator in which entrained impurities are removed, and the reusable powder is introduced into a pressurized tank by way of cyclically operating charging valves. Fresh powder is also added here on the basis of consumption, and then the processed powder is separated by means of cyclically operating charging valves and taken to the welding head by a separate compressed air push feed mechanism. In addition to the costly multiple-chamber charging and discharging systems for the granulated material, that is, welding flux, costly mechanisms for drying the delivery air are also needed to prevent caking of the powder in the push feed line. Moreover, centrifugal separators which promote wear by powder abrasion and which cannot be adjusted from the viewpoint of the limiting grain size to be separated are used in this case as well. In addition, the push feed employed presents the disadvantage that the delivery air leaving the welding head constantly discharges powder dust into the environment, even if only in small amounts.
In another welding flux processing system, although suction draft feed is used to eliminate the disadvantage last mentioned, a centrifugal separator abrading the working substance and a cyclically operating charging and discharging valve are required to deliver the welding flux serving as the working substance to the welding head. This design presents the further disadvantage that the wear-promoting impurities exhausted from the welding station along with the working substance still must flow through the greater part of the cycle before they are discharged from the cycle by a second centrifugal separator.